A wind turbine converts the kinetic energy of the wind into electrical energy through its rotor, drive train, electrical generator and converter. An electrical transformer converts the low voltage output from the converter into a high voltage output before it is sent to the substation at the wind farm. During the operation of the wind turbine, these major components and subsystems of the wind turbine dissipate a significant amount of heat to the surrounding air. So the clean, low humidity air inside the nacelle, where these components and the subsystems are mostly housed, has to be continuously either cooled and re-circulated (a closed air flow system) or replaced by fresh, clean, cooler, low humidity air (an open air flow system).
When the relative humidity (RH) of the surrounding air is high, the equipment corrosion rate is significant and it increases exponentially when the RH of the air is above about 65%. The equipment corrosion is exasperated by the presence of any water droplets and salt particles in the air. In the case of a wind turbine cooled with an open cooling air flow system, the equipment corrosion can be minimized by ensuring that the wind turbine is sealed except for the dedicated air inlets and outlets, and that the cooling air entering the wind turbine is clean (free of water droplets, dust and salt particles) and has a RH that is below the acceptable limit. The RH of the cooling air entering the wind turbine can be lowered either by heating it and or by dehumidification. As the cooling air flows through the nacelle from the air inlet to the outlet, its temperature continually increases and the RH correspondingly decreases because of the heat dissipation from the various components and subsystems in the nacelle. The sealing of the wind turbine helps prevent the unwanted high humidity ambient air entering the wind turbine and thus increasing the RH of the cooling air flowing through the nacelle. This helps minimize the equipment corrosion.
While the turbine is operating, the nacelle to rotor, the blade to rotor and the nacelle to tower interfaces move relative to each other. The rotor rotates with respect to the nacelle to generate the power from the wind. To generate optimum power, the wind turbine blades are adjusted, up and down, according to the wind speed. This adjustment comes from turning the each of the blades along its longitudinal axis (to pitch). Moreover, the nacelle is continuously yawed (rotated along a vertical axis) to ensure that the rotor is correctly oriented towards the wind direction. And all these interfaces typically contain dynamic seals to prevent the ambient air entry into the wind turbine or the clean air leakage out of the wind turbine. On the inside, the seals are exposed to the air that is inside the nacelle or the rotor. And on the outside the seals are exposed to the ambient air. It is well known that when air flows around a bluff body such as a cylinder, the air pressure along its surface varies significantly. A number of factors such as the dynamic loads on the sealing surfaces and the temperature variations and fluctuations affect the shape, the structure and thus the sealing ability of the seals. This results in either the ambient air entering the wind turbine or the air inside the wind turbine leaking out. Any humid ambient air into the wind turbine increases the chances of equipment corrosion.
The prior art on the corrosion control of the equipment inside an offshore wind turbine mainly consists of the use of dehumidifiers inside the wind turbine, corrosion inhibiting coating of the equipment, and cooling and recirculation of the clean, low humidity air inside the wind turbine and augmenting it with clean, low humidity ambient air. They do not specifically address the issue of the humid ambient air entry into the wind turbine or the clean air leakage out of the wind turbine through the dynamic interfaces.
While various other methods and systems have been developed in the past for preventing corrosion in the offshore wind turbines, there is still room for development. Thus a need persists for further contributions in this area of technology.